We will continue the work on the mode of action of the non-abrasive dust Dri-Die. This dust does not simply lead to death by desiccation. It has an effect on the epidermal cells that for most insect species is lethal even if water loss is prevented. Major effort at the present time is on trying to identify this effect on the epidermal cells. Currently this is primarily examination of cells by electron microscopy. Tests with more than 100 diverse species of insects has showed that insects are of three types in terms of their response to these dusts: most species are killed irrespective of whether water is lost or not, a few are killed only if excessive water loss is permitted (low ambient humidity), and larvae but not adults of two species are immune to effect irrespective of ambient humidity. There is currently no attractive explanation for these differences. BIBLIOGRAPHIC REFERENCES: Richards, A.G. & P.A. Richards. 1977. The peritrophic membranes of insects. Ann. Rev. Entomol., 22:219-240. Richards, A.G. & S.H. Seilheimer. 1977. The proventricular flanges in mosquito larvae. Entomol. News, 88:1-9.